In industrial process control systems, wireless networks have been widely deployed to support sensing and monitoring of industrial processes. These networks allow industrial processes to be monitored using wireless sensors without incurring the costs typically associated with wired devices. However, wireless sensors often need to be compliant with intrinsic safety standards in order to be used in certain applications. For example, wireless sensors may be required to satisfy a “zone 2” (intrinsic safety) or “zone 0” (highly hazardous) level of certification.
Often times, wireless sensors include radio frequency (RF) or other wireless radio boards, along with external antennas for better range performance. For a device to be intrinsically safe, a common constraint is that the antenna's ground and the radio board's ground are to be completely isolated by certain distances (approximately 0.5 mm for “zone 2” and approximately 3.0 mm for “zone 0”). Unfortunately, this type of arrangement disturbs the matching between the antennas and the radio boards, causing high RF or other losses due to ground discontinuities.
Normally, for lower RF frequencies (such as those operating at VHF bands), the grounds can be isolated using high-voltage coupling capacitors between the grounds. However, this approach typically cannot be used with higher frequencies (such as those greater than 1 GHz), which are very sensitive to grounding discontinuities. This approach also typically causes reductions in the transmit power and receiver sensitivity of the wireless sensors, such as by reducing the transmit power by approximately 3 dB. This affects the free space range of the wireless sensors and their reliability (which is often a major requirement for wireless sensor networks). In addition, since wireless sensors are often battery-powered devices, the reductions in transmit power and receiver sensitivity often require the wireless sensors to consume more battery power during operation, which reduces the operational lifetimes of the wireless sensors.